Kawachi H - Since tumor development occurs with an increase in the duration of the disease in patients with ulcerative colitis, the researcher analyzed the histopathological diagnosis of ulcerative colitis-associated neoplasia (UCAN). Problems in pathological diagnosis can be summarized into the following 3 categories: difficulty in discriminating UCAN from non-neoplastic inflammatory change; difficulty in discriminating UCAN from sporadic epithelial neoplasia (SPEN); and difficulty in histological grading of UCAN. Pathologists can make conclusive histological diagnoses without problems for most lesions. However, pathologists sometimes face diagnostic difficulties, particularly in cases of borderline or indefinite histology lesions, and thus need at least two experienced gastrointestinal pathologists to confirm the diagnosis. For the estimation of tumor depth and lymphovascular invasion in digestive tract cancers as well as in UCAN, confirmation is therefore usually preferable. Because UCAN has distinct features compared to SPEN, a multidisciplinary team should carefully discuss the treatment strategy for UCAN, especially in cases with histologically challenging lesions. While currently the most promising procedure for UCAN is surgical interventions such as total colectomy, recent advances in endoscopic diagnosis and therapy are expected to improve the current treatment strategy for UCAN in the future.